Method of testing and classifying bonded granular bodies



Feb.- 1, 1938. t R, ME N 2,107,186

Filed Dec. 11, 1930 INVENTOR Rom: L. MELTON I MW ATTORNEY Patented Feb. 1,1938

' METHOD OF TESTING AND cLAssmmo BONDED GRANULAR. BODIES Romie L. Melton, Niagara Falls, N. Y., assignor, by mesne assignments, to The Carborundum Company, Niagara Falls, N. Y., a corporation of Delaware Application December 11, 1930, Serial No. 501,538

Claims.

This invention relates to methods of testing and classifying bonded granular articles and the like and more particularly to methods of determining the t0ughness.of the bonded structure and the uniformity thereof.

The term toughness as used in the present application is that quality of a body which is exhibited in its resistance to disintegration due to impact blows imposed upon a relatively small area. The process of comparison of the toughness" of a number of abrasive bodies will involve a comparison of the penetration of an impact testing tool into a surface of the different bodies under like conditions of attack.

Abrasive bodies are regularly made in a variety of grades of toughness depending upon the particular work for which they are intended. An extended range of grades is obtained in artificial abrasive articles consisting of bonded silicon carbide or fused alumina by differences in the modes of manufacture; for example, variations in grade or toughness are obtained by variations in:

(l) The bonding materials;

(2) The methods of curing;

(3) The proportions of bond and granular abrasive; and

(4) The relative proportions of the amounts of abrasive grains of various sizes.-

Because of the effects of these and other variables on the toughness of the finished product, considerable care and skill are required in the manufacture of an abrasive article which is to have a predetermined degree of toughness that is best suited for a specific purpose; moreover, it has been found that the methods heretofore empioyed in testing the relative toughness of bonded abrasive articles did not give consistent results nor indicate satisfactorily the uniformity of the finished article.

The present invention provides a method for testing abrasive articles and the like as to their toughness and as to their conformity to specifications. Any simple testing machine that operates to remove a portion of the abrasive granules and bond in the form of detritus may be used in connection with my invention, but I prefer to use one which operates by impact and which has a bit or tool with a flat end. This tool is intermittently rotated and operated to deliver a predetermined number of impact blows against the surface to be tested and produce a recess therein. The depth of penetration of the tool into the test article is measured and is taken as an indication of the toughness of the article subject to certain considerations which are described in greater detail below. A machine of the character described is shown in patent of Romie L. Melton and John Fitzpatrick No. 2,003,863 issued June 4, 1935.

One of the chief difliculties in obtaining accurate comparisons of the toughness of various abrasive articles by the removal of a portion ofthe abrasive granules and bond (such as has been mentioned in the preceding paragraph) arises from the fact that the detritus formed collects in the hole or recess produced in the abrasive article. The collection of detritus in the hole impedes the penetrating action of the tool which is test piece without hindrance and permit an accurate determination to be made from a measurement of the depth of the hole when the cutting operation has been completed.

If the detritus be permitted to collect in the hole during the cutting operation, erratic errors occur in the readings of the machine. The detritus apparently has erratic and variable cushioning effects upon the penetrating action of the tool and precludes the accurate determination ofthe grade of the abrasive articles. 1

My invention is illustrated by the accompanying drawing in which:

Figure 1 is an elevation partly in section showing an impact tool which has penetrated an abrasive test piece after a certain number of impacts and means for applying a fluid stream for removing the detritus by treatment thereof between impacts.

Figure 2 is an elevation partly in section indicating a modified form of testing device in which the detritus is removed .by gravity.

Referring to the drawing in more detail the test piece Ill shown in Figure 1 is supported on its under side by a table II. The upper side of the test piece is struck a. predetermined number of blows by the lower end of a tool, cutter. or bit l2, which is removably mounted on a vertically movable plunger I3 and held in place by the set screw IS. The plunger I3 is always raised the same height preparatory to each stroke and is permitted to fall freely through a definite height through which it falls.

so that the tool delivers an impact against the test piece, the magnitude of the impact being determined by the falling mass and the height The detritus resulting from the above-mentioned operation is removed from the point of impact by a stream of fluid which is delivered at the point of impact of the tool under pressure by means of a nozzle ll or other suitable means. The fluid thus supplied by the nozzle may be air, gas, water, oil or the like or a mixture of these. The delivery of the fluid stream washes out the detritus from the hole formed by the tool and permits the latter to strike afresh surface at the time of each blow.

Tests show that if the detritus is allowed to remain in the hole during the drilling of the test hole, accurate results cannot be obtained. Even the small amount of dust or detritus produced in drilling -a very shallow test hole causes considerable and erratic errors in the readings of the machine' This is probably due to an erratic and variable cushioning effect of the detritusfrom hole to hole. For example, tests made upon the same test piece and under identical conditions but on days of high and low humidity show a considerable difference in the depths of penetration of the tool on such different days if the detritus is allowed to accumulate in the hole. Even tests made upon the same test piece upon the same day and with the same machine adjustment show an erratic variation in the depths of penetration from hole to hole. Tests made on a series of wheels made withincreasing propor- 'tlons of bond and therefore of increasing grades of toughness, may actually show a greater penetration in a tougher wheel than in a wheel of less toughness if the detritus is notremoved. These against the tool.

errors may be considerable and may result in inaccurate determination of the order of several grades. They are erratic and unpredictable and cannot be compensated for by any calibration of the machine. Exhaustive tests have shown that 'they cannot be eliminated by averaging a conthe abrasive or the abrasive article is projected Ineither case the detritus is automatically removed by gravity. In this modiflcation the abrasive body and tool may be moved relatively to one another in any suitable manner; for example, the abrasive body may be held stationary and-the tool be raised a definite distance to produce blows of uniform force at each blow, and after a predetermined number of blows have been delivered, the depth of the hole may be measured and taken as an indication of the toughness of the test piece. When thus inverted, the abrasive body does not require a stream of liquid or fluid to remove the detritus from the point of engagement inasmuch as the detritus will either fall out of the hole by gravity when formed or so little of it will remain in the hole as not to impede engagement of the tool with a practically clean surface of the test piece at the impact point of the tool.

A number of different fluids, such as compressed air, kerosene, lubricating oils, water and the like, have been used in practicing that form of this invention shown in Figure 1. Of these fluids compressed air proved to be the most practical, being effective in removing the de ritus, clean in operation, involving only small cost and permitting a more accurate determination of the depth of penetration of the impact cutting tool.

By means of my improved method of testing bonded granularbodies, or the like, it is possible to secure a true-analysis of the toughness and structural uniformity of abrasive bodies and accurately classify the same according to the work for which they are best suited.

I claim: I

'1. The method of determining the grade of a bonded abrasive article, which comprises subjecting a localized area of the article-to a predetermined number of impacts of predetermined magnitude of an impact cutting tool which breaks away abrasive particles and bond in the form of 2.'The method of determining the grade of i a bonded abrasive article, which comprises subjecting a localized area of the article to a prede-- termined number of impacts of predetermined magnitude of an impact cutting tool which breaks away abrasive particles and bond in the form of detritus and continually'removing such detritus by means of a fluid stream directed at the point of impact, and thereafter measuring the depth of the hole so produced. a

3. The method of determining the gradeof a bonded" abrasive article, which comprises subjecting a localized area of the article to a pre-. determined number of impacts of predetermined magnitude of an impact cutting tool which breaks away abrasive particles and bond in the form of detritus and relieving the cutting tool of the cushioning action of such detritus, and thereafter measuring the depth of the hole so produced. 4. The method of determining the grade" of a bonded abrasive article, which comprises subjecting a localized area of the article to a predetermined number of impacts of predetermined magnitude of an impact cutting tool which breaks away abrasive particles and bond in the form of detritus and continually removing such'detritus by means of a jet of compressed air directed at the point of impact, and thereafter measuring the depth of the hole so produced. I

5. The method of determining the grade" of a bonded abrasive article, whichpcomprises mounting the article to be tested with the test surface disposed downwardly, subjecting a localized area of the article to a predetermined number of impacts of predetermined magnitude of an upwardly directed impact cutting tool which breaks away abrasive particles and bond in the form of detritus and continually removing the detritus by gravity, and thereafter measuring the depth' of the hole so produced.

ROMIE L. MELTON. 

